Phase comparator for underwater signaling



Nqv. 21, 1950 J. a. KREER, JR 2,530,523

PHASE COMPARATOR FOR UNDERWATER SIGNALING Filed Nov. 1, 1944 3Sheets-Sheet 1 osc. 22s- INVENTOR BVJG. KREER, JR

H \1 ATTORNEY Nov.-21, 1950 .I. G. KREER, JR 7 2,530,523

PHASE coummpa FOR UNDERWATER" smmuuc Filed Nov. 1, 1944 s Sheets-Sheet 2OSCILLATOR 6S 6S VOLTAGE 5s ,5:

FIG. 2

OU TPU T VOL TA GE OF TRANSFORMER OUTPUT VOL 74 GE OF TRANSFORMER l6MODUL A TOR OUTPU T VOL TA GE PHASE FTER AAA

3/6 IN l/E N TOR 302 J G. KREER, JR.

A T TOR/V5 Y Nov. 21, 1950 Filed Nov. 1, 1944 PHASE COMPARATOR FORUNDERWATER SIGNALING J. G. KREER, JR 7 2,530,528

3 Sheets-Shet 3 VOLTXGE C YCLE OUTPUT VOL T465 CYCLE FOR CURVES 14,8 ANDC.

OSCILLATOR VOLTAGE FOR cunvss 4,5 AND c VOLTAGE OUTPUT OF /5 VOLTAGEOUTPUT OF /6 MODULATOR aurpur VOLTAGE IN ME N TOR y JG. KREE/P, JR

A T TORNE Y l atented Nov. 21 1.950

PHASE COMPARATOR FOR UNDERWATER SIGNALING John G. Kreer, Jr.,Bloomfield, N. l, assignor to Bell Telephone Laboratories, Incorporated,New York, N. Y., a corporation of New York Application November 1, 1944,Serial No. 561,448

2 Claims.

This invention relates to location of objects.

A purpose of the invention is to ascertain the direction of a distantobject from a reference point.

This may be done by receiving a signal wave from the object in each of apair of directional receivers mounted, for example, side by side nearthe reference point, which may be a point midway between the receivers,and deriving the desired direction indication from 0, the phasedifference of the wave at the two receivers.

The receivers may be, for example, hydrophones on a surface vessel; andthe object may be, for example, a submerged or partly submerged object,as for instance an enemy submarine. Then the received signal wave maybe, for example, an echo or reflection from the distant object of anunderwater supersonic signal wave originated on the surface vessel anddirectionally transmitted from it as a short wave-train.

The phase angle is dependent in magnitude and sign on the direction,from the reference point, of the submarine or object from which the waveis received. The receivers are of such design that there is a uniquecorrespondence between 0 and the orientation angle of the receivers withrespect to this direction, (1. e., with respect to the direction fromwhich the echo or signal wave approaches the reference point), at leastwhen such orientation angle is contained within the principal lobe ofthe directional response pattern of the receiver system. Outside thislobe the sensitivity of the pick-up is so small as to make theprobability of confusion negligible. The receivers may be rotatabletogether in azimuth, about the reference point, so that they can betrained on the object, to make the value of 0 zero. If they are trainedto the right or left of the object, 0 will differ from zero. Means maybe provided for deriving from the received waves a voltage which is anodd function of 0; and this voltage may be utilized to obtain anindication of whether the receivers are trained directly on the object,or to the right of the object, or to the left of the object.

In accordance with a feature of the invention,

the means for deriving the desired voltage which,

ficulty is encountered in determining the bearing of the target by theusual method which involves determination of the orientation of thereceiver at which maximum echo is received, inasmuch as successive wavetrains or pings produce echoes that may vary as much as 20 decibels, forexample.

Therefore, an object of the invention is to provide means fordetermining the bearing from the phase parameter of the signal,independently of the amplitude of the signal.

Other objects and features of the invention will be apparent from thefollowing description and claims:

Fig. 1 is a circuit diagram of a system embodying one form of theinvention;

Figs. 2 and 3 show voltage diagrams explanatory of the operation of thesystem of Fig. 1; and

Figs. 4 and 5 show modifications of the system of Fig. 1.

Fig. 1 shows a direction indicator circuit or hearing deviationindicator circuit embodying a specific form of the invention suitablefor use, for example, with underwater sound echo rangng equipment on asurface vessel. The circuit comprises a projector 3 for transmitting asound beam and receiving an echo of the sound from a distant object ortarget, and a cathode-ray oscilloscope 12 for indicating the sign, ordirection, of the deviation of the pointing, or bearing, of theprojector from the bearing or direction of the target. The projector ortransceiver 3 may be, for example, a crystal type of projector, such,for instance, as that disclosed in Arthur C. Keller Patent 2,417,830,March 25, 1947 for Compressional Wave Signaling Device. Its right andleft halves R and L are two receivers or hydrophones adapted to receivean echo from an enemy submarine or other submerged or partly submergeddistant object or target (not shown).

The projector sends out a signal wave to be reflected or echoed from thetarget and thereafter received by the projector serving as echoreceiving means. Each of the projector halves comprises a crystal array,and electromechanical action of the crystals translates the receivedsound into electrical energy. The projector face is indicated at 5. Itmay be about ten inches in diameter, for example, and is a verticalplane surface which projects the sound wave and is presented to theecho. The projector is suspended below the ships keel, from the lowerend of the projector training shaft Illa This is a vertical shaft towhich the projector is attached and by which the projector may berotated clockwise and counter-clockwise, in azimuth, to change theprojector bearing, i. e., the direction in which the projector faces.The extended axis of the shaft it! passes between R and L and throughthe center of the projector face.

The projector transmits into the water a pulse or short wave-train ofsound of a frequency of 24 kilocycles per second, for example,translating electrical energy of that frequency received from driveramplifier ll into the sound energy and emitting the sound into the waterin a unidirectional beam. For this transmission, a relay I2 is operatedto connect the output of the amplifier to the two halves of theprojector in parallel. Immediately after the transmission of the shortpulse into the water, the relay is deenergized, to disconnect theprojector from the amplifier and connect R and L to input transformersI5 and I6 respectively of an input modulator 2|], so that when thetransmitted sound pulse strikes a submerged object and a portion of thesound is reflected from the object as an echo and is picked up as suchby the projector and translated into electrical energy by the projector,this electrical energy is fed to the modulator 26 for utilization indetermining the direction of the object as indicated hereinafter.

In sending and in receiving, the projector is highly directional and maybe highly efiicient over a frequency range of 22 to 28 kilocycles persecond, for example. In sending, it transmits the sound pulses into thewater in a beam pattern with the direction of the highest intensityperpendicular to the projector face, the intensity decreasing rapidly oneither side and being small or negligible at the rear; and in receivingits response is correspondingly directional.

The circuits 6 and 1 from the halves of the projector to the switchingelements of relay l2 may conveniently be made through slip rings (notshown), carried by the shaft 10, and transformers (not shown) may matchthe impedances of the crystal arrays to the impedances of circuits 6 andI. The shaft can be rotated to orient the projector in azimuth,clockwise and counter-clockwise, to search for a target. When theprojector is trained on the target, the echo received by the two halvesof the projector will have substantially no difference in phase at thetwo halves. On the other hand, when the projector is trained to theright or left of the target, the phase of the received echo at theprojector half R will differ from the phase of the received echo at theprojector half L, the magnitude and sign of the phase diiferencedepending on the magnitude and sign, respectively, of the anglerepresenting the deviation of the bearing of the projector from thebearing of the target, i. e., the angle between a vertical plane normalto the projector face and the vertical plane passing through the targetand the center of the projector face. The arrangement of the system maybe, for example, such that one degree change in projector bearingproduces degrees change in phase diiference between the two projectoroutput voltages. Then the maximum usable angle of projector bearingdeviation in determining the bearing of the target from the phase d'fierence between the two projector output voltages may be about 6degrees which produces a change of about 90 degrees in that phasedifference.

When the projector is pointed directly at the distant reflecting objectthe echo will be strongest and moreover, as explained hereinafter willnot cause the cathode-ray spot on the screen of the oscilloscope 42 tomove appreciably to the right or left. When the projector is trained tothe right or left of the distant object the length of the path of thereceived echo is unequal for the two halves of the projector, whichresults in a difference in phase of their electrical outputs. Theseoutputs are compared as indicated hereinafter, being utilized to causethe oscilloscope spot to move to the left or right and thereby indicatewhether the bearing of the distant object is to the left or right ofthat of the projector. By repeatedly projecting sound pulses andsuccessively observing the strength of echoes received and also thechanges in the amplitude and direction of the deflection of theoscilloscope spot, with changes in bearing of the projector, thedirection of the distant object may be determined, and followed if thetarget is moving. As explained hereinafter, the strength of the echoesreceived may be observed, for example, aurally by means comprising areceiver circuit 26 and loudspeaker 53.

The driver amplifier ll receives its 24-kilocycle input from a modulator2|, which produces a z i-kilocycle wave by combining the 15fl-kilocycleoutput wave from driver oscillator 22 with a l'l l-kilocycle output wavefrom oscillator 23.

The relay l2 may be operated by a keying circuit 32 which controls thecurrent through the relay winding. When the relay is in the nonoperatedposition so contacts connect R and L to I5 and it, another set of itscontacts connects a terminating resistor 24 across the input of thedriver amplifier I! to prevent it from singing; When the relay isoperated by the keying circuit so R and- L are disconnected from 45 to[6 and connected in parallel to the output of the driver amplifier, insequence the terminating resistor 24 is removed from the driveramplifier input and the driver amplifier input is connected to themodulator 2|. With this sequence of switching, the changeover isaccomplished when currents flowing through the relay contacts are low.

The circuit of Fig. l comprises: a push-pull oscillator 25 whosefrequency may be nominally 225' cycles per second; for example, but maybe slightly adjustable for a purpose disclosed hereinafter; a receivercircuit 26 fed from modulator 20 and feeding a two-stage audio frequencyamplifier 2? including a gain adjusting potentiometer 28' and afrequency discriminator 29; a detector or amplitude demodulator 30 fedfrom amplifier 2i and including a band-pass output filter 3 I; anamplifier tube 35 comprising a buffer amplifier section 36 fed fromfilter 3| and a second buffer amplifier section 3:! fed from theoscillator 25 through conductors 38; a rectifier ill having conjugateinputs from the buffer amplifiers 35 and 31, the input from amplifier 36being applied through conductors 36 and the input from amplifier 37being applied through conductors 3'5; a balanced direct currentamplifier 4| fed from the rectifier 3 3; acathode-ray oscilloscope 42having its horizontal deflection coils 43 and 44 fed from amplifier lland having its vertical deflection coil 45 fed from a sweep circuit 45,the circuit 655 including amplifier tubes 41 and 43 and being controlledby the relay I2 through conductor 52. v

As explained hereinaften the circuit 45 causes the cathode-ray spot tosweep vertically from the bottom of the screen to the top, andthe signalcauses it to be deflected horizontally during this vertical sweep, thehorizontal deflection of the spot during its vertical travel providingan indication of the direction of the projector deviation from on-targetbearing As will appear from description hereinafter of operation of thesweep circuit 46, a range rheostat 53 provides for selection of thevertical sweep period. A period is selected that will correspond withthe time elapsing between the start of successive pulses or wavetrainsof the sound transmitted from the projector, or in other words willcorrespond with a vertical rate of travel that (for a given sweepamplitude) will depend on the pulsing rate or pulsing frequency, i. e.,on the number of pulses or wavetrains transmitted per unit of time. Thepulse duration is relatively short. It may be, for example, about 35milliseconds for target ranges under a few thousand yards, and 150milliseconds for ranges of five or ten thousand yards. The intervalsbetween pulses may be of the order of one to ten seconds, for example.For instance, they may be about 12.5 seconds for target ranges between4,500 and 10,000 yards, and 1.25 seconds for target ranges below 1,000yards, and for intermediate ranges may approximate 1.25 seconds perthousand yards of range. In general, it is desirable to pulse asfrequently as the range of the target (i. e., the distance to thetarget) will permit, and therefore to increase the frequency of thepulsing as the target is approached.

The receiver 25 comprises: an input amplifier 55 fed from the modulator20; a modulator 56 fed from the amplifier 55 normally tuned to 24kilocycles, for example, and from the oscillator 23, normally tuned to174 kilocycles, for example; an amplifier fed from the modulator 56; amodulator 58 fed from the amplifier 57 and from an oscillator 63 whosefrequency may be 150.8 kilocycles, for example; a modulator output bandfilter 6! whose pass-band may extend, for example, from 100 cycles persecond to 2,000 cycles per second; and an audio amplifier 62 which mayfeed a loudspeaker 63 as well as the gain control potentiometer 28 ofthe audio amplifier 21.

The frequency. discriminator 29 comprises condenser 65 and resistor 53,and has attenuation decreasing with frequency increase throughout thefrequency range of the output of the receiver 25, to convert the phasemodulated output of receiver 26 into an amplitude and phase modulatedwave for detection in amplitude demodulator 30.

The audio amplifier 21 includes resistance-capacity coupled tubes 58 and69. Across the output circuit of tube Bis is a circuit comprising apotentiometer resistance 13 in series with direct current blockingcondensers H and 12. The resistance Iii and an adjustable contact 53form a pctentiometer E4. When a signal (an echo) is received byprojector 3, tube 69 produces an audio frequency voltage across thepotentiometer resistance 10. The portion of this voltage appearingbetween adjustable contact '33 and condenser '52, i. e., thepotentiometer output voltage, is introduced in the cathode-grid circuitof the oscilloscope 42. It automatically increases the intensity orbrightness of the oscilloscope spot perceptibiy during reception ofsignals.

The cathode-grid circuit of the oscilloscope extends from the cathode ofthe oscilloscope through conductor 15, contact "53, the lower portion ofthe potentiometer resistance 10, conductor 75, an adjustable contact itof a potentiometer 78, the lower portion of the potentiometer 7'8,ground, conductor 19, two normally closed contacts of relay l2, andconductor 80, to the os cilloscope grid. In series in this oscilloscopecathode-grid circuit are introduced the voltage across the lower portionof the potentiometer 10 and the voltage across the lower portion of thepotentiometer 18. This voltage across the lower portion of thepotentiometer 18 is adjustable by the potentiometer contact H, and isdue to current flowing through the potentiometer from the 220-voltterminal of power supply source 13. The contact ll may so adjust theintensity of the spot on the oscilloscope screen that the spot is justperceptible in the absence of signal reception. The power supply sourceB is shown as a battery for the sake of simplicity, but in practice isordinarily a rectifier output circuit, and may be any suitable directcurrent source.

Thus, normally the oscilloscope grid is at ground potential and thecathode is maintained positive with respect to ground by thepotentiometer contact Ti. By adjusting this contact the bias on the gridmay be changed and the intensity of the cathode-ray spot increased ordecreased. On receipt of a signal the voltage introduced in the circuitbetween cathode and ground by potentiometer it varies the cathodepotential, increasing the brightness of the spot during the alternatehalf-cycles in which the cathode potential is reduced and therebycausing an apparent brightening of the spot. As will become apparentfrom description hereinafter of operation of the circuit of Fig. 1, whena signal is received with the projector off-target, due to 225-cyc1eamphtude modulation appearing in the signal the oscilloscope tracebecomes a broken line. The degree of brightening of the oscilloscopespot can be varied by adjusting the potentiometer M.

During the transmitting condition of the circuit of Fig. l, relay [2 isoperated. When the relay operates; it transfers the oscilloscope gridlead 80 from grounded conductor 19 to a conductor 8| connected through aresistor 82 to the -l00-volt terminal of the source B. This appliesabout 90 volts of bias to the grid, to cut off the cathode-ray and thusextinguish the cathode-ray spot. The resistor 82 protects the 100-voltsource, and may have a value of about 70,000 ohms, for example. Afiltering or by-pass condenser 83 is shown connected from the -190-voltterminal of the source B to ground.

A resistor 85 connecting the grid of the oscilloscope to ground preventspossibility of the grid being a. floating grid. This resistance may havea value of the order of half a megohm, for example.

Plate voltage for the oscilloscope 42 is supplied across resistor 81,from a rectifier (not shown),

7 for example, through a resistance-capacity filter 38. The rectifiermay maintain a, nominal voltage of 6,000 volts, for example, across theresistance 81. This resistance improves the regulation of the rectifierby helping to keep the load constant, and discharges the high voltageacross the condensers of the filter when the alternating current supplyto the rectifier is disconnected.

The vertical centering of the cathode-ray is adjusted by a potentiometer89 and the horizontal centering by the potentiometer 90. Adjustment ofthese potentiometers varies the current flowing from the 220-voltterminal of source B through the vertical and horizontal centering coils9| and 92. The potentiometer 89 is set to position the cathode-ray spotnormally at the top of the screen. A potentiometer 93 controls thecurrent flowing from the 220-volt terminal 7 of the source B through thefocussing coil 94 for the cathode-ray.

For clarity, a specific sweep circuit 46 will be described withconstants and operating voltage and currents given concrete values asexamples of values that may be used.

Tubes t? and 68 of the sweep circuit 46 conduct alternately. When relayI2 operates, current from the 240-volt terminal of source B flowingthrough tube 68 and coil 35 moves the oscilloscope spot swiftlydownward. (As indicated above, while the relay is operated, theoscilloscope grid is biased to cut oi? the cathode-ray, the spot then isnot discernible.) When the relay is released, current irom the groundterminal of the source B flowing through coil 55 in the oppositedirection and through tube ll moves the spot upward relatively slowly tothe top of the screen, with the aid of coil 9!.

In this sweep circuit, current flows from the ground terminal of thesource B through the deflecting coil 45 and a resistor N15, to the 100-volt terminal of the source B, creating a voltage drop of about 60 voltsacross resistor I91. Current also flows from the ground terminal ofsource B through a resistor 32 andthrough the resistance of apotentiometer IM to the -100-volt terminal of source B, making thepotential of the junction of I82 and IM, and therefore the potential ofthe cathode of tube 31, about -75 volts (with respect to ground).

In considering operation of the sweep circuit, the starting point may betaken as the instant preceding the operation of the relay 42 to startthe next sweep of the oscilloscope spot. At this instant the spot is atthe top of the screen and the conductor 52 is open circuited. The tubeis in a conducting condition, because the bias on the grid, supplied bycondenser it as presently will appear, will have been largely dissipatedthrough a series circuit comprising resistor Hill, the resistance ofpotentiometer its, and a relatively high resistance formed by a resistorIt? and the range rheostat Therefore, due to the voltage drop createdacross resistor H)! by the current flowing therethroug'h from coil Q5,current is flowing from the junction of coil 5 and resistor ifil,through interstage coupling resistors H38 and I59, tube 4i, and theresistance of the potentiometer we, to the l volt terminal of the sourceB. This current flow through Hi8 and IE9 produces a negative biasvoltage across the grid and cathode of the tube 48. The value of thisvoltage will depend on the adjustment of resistor I68 but will usuallybe 30 volts or more. This voltage cuts oh the plate current of the tube38. The value of the current flowing from the ground terminal of sourceB through coil 45 and resistor It] is about 25 milliarnperes, which issomewhat less than that-needed to move the cathode-ray spot from thecenter of the screen to the top of the screen. The spot is therefore setat the top of the screen by adjust ment of the vertical centeringcontrol as. The junction of the grid of tube 4-? and condenser M8 is atabout the potential of the junction of resistances I02 and ltd, thesetwo junctions being connected through resistances I01 and 53 in series.The tubes! may be of type 'GSJ'FGT-and the tube 48 of type GVGGT. Thedirect current resistance of coil 45 may be 1,200 ohms. The respectivevalues of resistances El, 102, 104, l-ifl, I68, I89 and 53 maybeapproximately 2500 ohms, 155600 ohms, 2,000 ohms, 91,000 ohms, 50,000ohms, 27,0'00 ohms, and 834,000 oh'ms. The

8 capacitance of condenser I06 may be 1 microfarad.

When the keying circuit 32 operates relay l2, conductor 52 connects thejunction point of the grid of tube 4''! and condenser N36 to theadjustable contact of potentiometer I84. This makes that junction pointmore negative with respect to ground, consequently making that junctionpoint substantially negative with respect to the cathode of tube 31,which reduces the current through resistances i438 and I09 and alsocauses condenser ms to begin charging, the charging.

current flowing from the ground terminal of source B through coil 45,condenser I06, conductor 52 and adjustable contact of potentiometer IMto the -100-volt terminal of source B. The reduction of current throughresistances 108 and its renders tube 38 conducting, so current flowsfrom the 240-volt terminal of source B through tube t8 and resistor Ifllto the 100 -.-volt terminal of source B and thus increases the voltageacross lill. The voltage to which the comdenser I06 charges when relay12 operates and also the negative potential which the junction of thegrid of tube 4'! and condenser I06 assumes with respect to ground andtherefore the negative grid-cathode or bias voltage of tube 41 dependson the setting of the contact of potentiometer I'M, being greater thenearer the contact is set to the 'i00-volt terminal of source B. Thevoltage to which the condenser I66 charges depends, moreover, on thechange in voltage across resistor ml which is due to considerableincrease in plate current of tube 48 when the plate current, of tube 4'!decreases or cuts off. The larger the value of resistance IN, the higherthe voltage to which the condenser charges. With the proper setting ofthe contact of po tentiometer Ills, the negative bias on the grid oftube ll will be sufficient to cut ofi the plate cur-.- rent of tube 4?.When this occurs, the bias on the grid of tube 58 is removed. With theconsequent sudden drop in the plate-cathode resistance of tube 48, thecathode potential risesiabove ground potential. In other words, theefiect of the plate voltage supplied from the ground and 240-voltterminals of the source B is transferred to coil 45 in the cathodecircuit and in coil 4.5 opposes and exceeds the eifect of the voltagesupplied from the ground and 1.00-volt terminals of the source B, sothat about 31 milliamperes of current flows through coil 45. Thedirection of this current is from the cathode of tube 48 through coil45, to ground. The direction of ourr rent flow .has therefore beenreversed in the coil and the cathode-ray spot (not actually visible atthe time) is moved from the top of the screen to the bottom so that itis then in position to begin its vertical sweep upward. The circuit willremain in this condition as long as relay I2 is in the operationposition.

When the keying circuit .32 deenergizes the windin of relay E2, therelay opens the connection 52 between the condenser I and the contact ofpotentiometer Hi l. Immediately upon this opening of the chargingcircuit, the condenser starts to discharge' throug-h the path comprisingresistor till, the resistance of potentiometer 1M, and the highresistance circuit through 5'3 and H17, the voltage drop across 53 and 191 appearing as negative biasing voltage between the grid and cathode oftube 41. The condenser will continue to discharge until its junctionwith the grid of tube 41 again reaches the potential of the cathode oftube :41, and the length of time required to accomplish this will dependon the adjustment of range rheostat 53, i. e., on the amount ofresistance of the rheostat 53 which is in circuit. As the condenserdischarges, the negative bias on the grid of tube 41 graduallydecreasing, the tube becomes again conducting. As the plate current ofthe tube 4! increases from zero, a voltage drop again builds up acrossresistors It?) and I09, causing tube 48 to return gradually to itscondition of plate current extinction. The current flow through coil 45will therefore gradually decrease from 31 milliamperes to zero, and thenincrease with reversed sign or direction until it reaches its formervalue of approximately 25 milliamperes. The cathode-ray spot thereforewill sweep from the bottom of the screen to the top, and its rate oftravel will depend on the time required for the current in the coil45'to decay to zero and build up to its full value in the oppositedirection.

The approximate timing of the upward sweep or travel is accomplished byadjustment of the resistor network comprising resistor IE1! and rangerheostat 53. Finer adjustment may be obtained by the potentiometer I04,which controls the sweep amplitude and rheostat I03, which controls thesweep rate.

The setting of the potentiometer I94 adjusts the voltage towhich thecondenser H16 will be charged when relay I2 closes conductor 52; and thesetting of this potentiometer also adjusts the grid-cathode bias voltagethen applied to tube 41. If the potentiometer contact were set too nearthe l-volt terminal of the potentiometer, the condenser would be chargedto a voltage too great, and consequently the grid of tube 41 wouldremain near a plate current cut-ofi potential for a period after the endof the transmission of the sound pulse, 1. e., after the opening ofconductor 52, and the upward sweep would begin too late. If thepotentiometer contact were set too far from the 100-volt terminal of thepotentiometer, the negative biasing voltage applied between the grid andcathode of tube 4'! through conductor 52 upon the operation of relay I2would be so small that the grid of tube 21 would not entirely extinguishthe plate current of tube 47, and consequently the plate of tube 48would not draw sufiicient current to cause the cathode-ray spot to moveall the way to the bottom of the screen. With proper adjustment or"potentiometer ms, the spot will be brought to the bottom of the screenand its vertical sweep upward will start at the instant the relay I2 isreleased.

The rheostat IE8 adjusts the sweep time so that the spot just completesits travel. to the top of the screen when the relay I2 operates to startthe next sweep. With any given setting of the range rheostat 53, thelength of time current will flow through rheostat I538 and resistor itswill be constant, since, with the keying circuit 32 op erating the relayI2 at a given sound pulsing rate, the time between operations of therelay is constant. The value of voltage this current will develop on thegrid of tube 48 in this fixed length of time will depend largely on theamount of resistance the rheostat introduces in the circuit. Byadjustment of this rheostat this grid bias can be made to reach itsultimate plate current cutoff value just as the relay operates to startthe spot downward in the next sweep. Under this condition thecathode-ray spot will have just reached the top of the screen and willbe in the proper position to be returned to the bottom of 10 the screenfor the start of the next upward sweep.

The input modulator 2!] comprises a varistor that includes fourcopper-oxide rectifier units I2I, I22, I23, and I24, which may be alike,each forming an arm of a bridge circuit and all pointed in the samedirection around the circuit.

The secondary windings of the input transformers I5 and I6 of themodulator 2e are connected in series across the primary winding ofoutput transformer I25 of the modulator. To one end of that primarywinding is connected the junction of arms I2I and I22, and to its otherend is connected the junction of arms I23 and I24. A conductor I 23connects the junction of the secondary windings of transformers I5 and I6 to the center of an output coupling coil I21 of the oscillator 25; andthat coil is connected between the junction of arms I2l and I24 and thejunction of arms I22 and I23, to supply a 225-cycle wave from theoscillator to the modulator 20.

As indicated above, during the receiving condition of the system R isconnected to IE and L is connected to IE; and as explained below, thevaristor modulator 20 supplied with 225-cycle voltage from theoscillator 25 short-circuits the secondary winding of IS during thosehalf-cycles of the 225-cycle voltage in which the upper terminal of coilI 2'! is positive with respect to its lower terminal, which may becalled the positive half-cycles, and short-circuits the secondarywinding of I5 during the alternate halfcycles, i. e., the negativehalf-cycles. The output of the modulator 29 is primarily the voltagefrom R or L, except for the transition period at the zero voltage pointof the oscillator voltage cycle when the oscillator voltage is causingthe varistor to transfer the short-circuit from one input transformer tothe other. During this transition time or period the modulator output isa combination of the two voltages from R and L, and as shownhereinafter, is of frequency greater or less than 24. kilocycles, theamount and direction of frequency shift depending on the amount anddirection of phase difference between these tw voltages.

The 225-cycle oscillator voltage that is applied to the varistor 29 hasa root mean square value of .4 volt, for eXample and since the signalvoltage received at the varistor is at most only a few millivolts, forexample, the oscillator voltage controls the resistance of thecopper-oxide units of the varistor. When the oscillator voltage isapplied to the varistor, the resistance of the copper-oxide discs variesfrom about 4 ohms in the conducting direction to 6,000 ohms in thenonconducting direction with a very large change in resistance takingplace during the time in the oscillation voltage cycle when the voltageis passing from positive through zero to negative or vice versa.Therefore, except for a. small part of the voltage cycle around the zerovoltage point, one-half of the varistor or the other half has aresistance that is low enough to be considered a short circuit.

During the positive half-cycle of the voltage of the 225-cycleoscillator, i e., when the 225-cycle oscillator voltage applied to thevaristor is in such direction that the upper terminal of coil i2? ispositive with respect to its lower terminal. the copper-oxide discs inarms I23 and I24 short-circuit the transformer I6, the impedance of thetwo halves of the coil I2'I in parallel op posing relation beingnegligibly low for the 24- kilocycle frequency, and the output of themodaaooaoas ill dilator, delivered to transformer 125, will he thevoltage derived from R and i5. 011 the "next half-cycle of theoscillator voltage, i. e., the negative half-cycle, the lower terminalof coil i2? is positive with respect to its upper terminal and thetransformer I5 is short-circuited by the copper-oxide units in arms I21and H2, so the output voltage of the modulator, delivered tc transformerI25, will be the voltage derived from L and it. During the period oftime extending :from shortly before the end of the positive half- .cycleof the oscillator voltage to shortly after the beginning of the negativehalf-cycle the varistor resistance across the secondary winding oftransformer it increases rapidly from a shortcircuit condition or valueand the resistance across the secondary winding of transformer l5decreases rapidly toward a short-circuit condition. The output voltageof transformer l5 will therefore gradually decrease to a negligibleamount while the output voltage of transformer It is rising to amaximum, and the modulator output will be a combination of these two"voltages. These conditions are illustrated in Fig. 2,

which indicates the effect of the 225-cycle oscillator voltage on inputand output voltages of the modulator. In Fig. 2 the portion of the\oscil lator voltage cycie marked 16S corresponds to the timetransformer it is short-circuited, and the portion 155 corresponds tothe time transformer I5 is short-circuited.

As noted above, when the system is adjusted to transmit a 24- kilocyclesound pulse from the projector and the projector bearing is the same asthe target bearing, the voltages produced in the two projector halves Rand L by the echo signal will be in phase; and with the projectortrained off the target, the returning 24-kilocycle signal will producevoltages in R and L that are out of phase "in proportion to the anglethe projector is trained from the on-target position. In other words,with the projector trained on the target the two output voltages of theprojector are in phase and in the off-target condition they are out ofphase, the magnitude and sign of their phase difference depending on theextent and direction the projector is trained in azimuth from thebearing of the target. There will therefore be one of three voltageconditions existing in the modulator output. These are illustratedqualitativelyhy three sets of curves, A, B and C, in Fig. 3, whichindicate the phase and frequency of input and output voltages of themodulator, these curves corresponding in time to a transition of theoscillator voltage from "its positive halfcycle to its negativehalf-cycle as shown by curve D.

Curves A illustrate the formation of the moduiator output when theprojector is trained on the target and the output voltages oftransformers l5 and I 6 are consequently in phase. At a point of themodulation oscillator voltage cycle where the varistor hasshort-circuited transformer It, i. e., at a time preceding that whichcorresponds to the depicted portion of curves A and D, the modulatoroutput consists of the output delivered from transformer l5. As theoscillator voltage progresses toward zero, a time corresponding to theleft-hand edge of the figure is reached when the varistor resistanceacross transformer It begins to rise and the resistance acrosstransformer 15 begins to decrease. Voltage from both transformers beginsto appear in the modulator output, (i. e., voltage from 5 begins toappear in the modulator output and is combined with the voltage from I15appearing in the modulator output) This process continues until, at thezero voltage point of the oscillator voltage cycle, maximum voltage isde livered to the modulator output, as a result of the contributions ofboth input transformers. ,As the oscillator voltage passes from zero andtakes values of an opposite sign, (the negative sign), the resistanceacross transformer it gradually decreases until a time, subsequent tothe time corresponding to the right-hand edge of the figure, arriveswhen the modulator output is that delivered by the input transformer it.After the oscillator voltage with the negative sign passes maximumamplitude, it progresses toward zero and the above process reverses, themodulator output again becoming a maximum (as a result of thecontributions from both input transformers) when the oscillator voltagebecomes zero. As the oscillator voltage proceeds from zero to itsmaximum positive value, the modulator output again becomes the outputfrom transformer 55.

Since, with the projector trained on the target, the voltages producedin the two projector halves R and L by the '2e-hilocycle echo signal arein phase, the resultant voltage produced across their secondary windingsor delivered to the modulator output transformer I during the time oftransition from one-half (positive or negative) of the modulationoscillator cycle to the next half will be in phase with these voltagesand be of their frequency, but will be of increased amplitude withmaximum increase occurring .at the zero voltage point of the oscillatorvoltage cycle. The output of the modulator during an on-target conditionis therefore a voltage of a frequency of 24 kilocycles per secondincreasing in amplitude momentarily at the rate of 456 times a second(i. e., at the frequency at which the instantaneous value of the225-cycle oscillator voltage passes through its zero value), or in otherwords with amplitude modulation at a frequency of 450 cycles per second.

Curves B of Fig. 3 illustrate the formation of the modulator output foran oscillator voltage transition period which is the same as in the caseof curves A; but in the case of curves B the projector hearing has beenso shifted, i. e., the projector has been trained oiT-target in suchdirection and to such extent, that the voltage output of transformer Itis ninety degrees behind that of transformer I5. Thus, curves Billustrate the formation of the modulator output during a period inwhich its constitution changes from one voltage, viz., the voltagedelivered by transformer I5 (withthe varistor short-cireuitingtransformer it), to a voltage lagging behind said one voltage bydegrees, viz., the voltage delivered by transformer 16 (with thevaristor short-circuiting transformer l5). As the modulator outputvoltage transition from the output of transformer 15 to the output oftransformer l6 progresses, the consequent progressive shift in the phaseof the modulator output voltage, from a phase which is that of theoutput voltage of transformer I5 to a phase which is that of the outputvoltage of transformer I6, is tantamount, during the first half of thetransition period, to .a progressive increase in the wavelength, or aprogressive decrease in the frequency, of the modulator output (from itswavelength and frequency when they are those of the 24-kilocycle outputof transformer l5), and is tantamount, during the second half of thetransition period,

to a progressive decrease in the wavelength, or increase in thefrequency, of the modulator output, (to its wavelength and frequencywhen they are those of the 24-kilocycle output of transformer 16). Thusthe modulator output during its transition period corresponding to thetransition from the positive half-cycle of the oscillator voltage to thenegative half-cycle, decreases in frequency from 24 kilocycles until itreaches a minimum value at the zero voltage point of the oscillatorvoltage cycle, and then gradually re-- turns to 24 kilocycles.Analogously, (for projector bearing deviation of the same sign) themodulator output, during its transition period corresponding to thetransition from the negative half-cycle of the oscillator voltage to thepositive half-cycle, increases in frequency from 24 kilocycles until itreaches a maximum value at the zero voltage point of the oscillatorvoltage cycle, and then gradually returns to 24 kilocycles; becauseduring this transition period the phase of the modulator output voltageprogressively shifts from a phase which is that of the output voltagetransformer It to a phase which is that of the output voltage oftransformer I5, 90 degrees ahead. (This may readily be seen from curvesC, described below, by considering the solid line curve C to be a dashline curve representing the output voltage of transformer l6 andconsidering the dash line curve C to be a solid line curve representingthe output voltage of transformer l5.) Therefore, the modulator outputduring the assumed off-target condition is a 24-kilocycle voltagealternately decreasing and increasing momentarily below and above 24kilocycles, or in other words, is a 24-kilocycle voltage decreasingmomentarily to a lower frequency, then returning to 24 kilocycles, nextincreasing for a moment to a higher frequency, then returning to 24kilocycles, and repeating the whole process at the 225-cycle rate of theoscillator voltage cycle as long as the echo signal from the target isbeing received and the projector bearing retains its assumed value; andthe amount the modulator output frequency deviates above and below theaverage value of 24 kilocycles depends upon the magnitude of the phasedifference between the two projector voltages and consequently upon themagnitude of the angle constituting the projector bearing deviation, i.e., the angle through which the projector is trained off-target.

Moreover, this same character of modulator output will be retained ifthe sign of the projector bearing be reversed (i e., if the projector betrained through its on-target bearing to the opposite off-targetdirection), except that, due to changed phase relation of the twoprojector voltages, at any given transition point of the oscillatorvoltage cycle the sign of the deviation of the modulator outputfrequency from 24 kilocycles will be the reverse of the sign thatobtained before the change of the projector bearing. This is readilyseen from curves of Fig. 3, which are for the case of this changedbearing, the magnitude of the projector bearing deviation beingconsidered to be 90 degrees, 1. e., the same as before the change in thesign of the deviation.

These curves C illustrate for this changed projector bearing, theformation of the modulator output for an oscillator voltage transitionperiod corresponding to that for curves A and B, i. e., a transition ofthe oscillator voltage from its positive half-cycle to its negativehalf-cycle, as shown in curve D. Thus, the curves C illus- .laggingvoltage to the leading voltage, in the transition period the modulatoroutput frequency increases from 24 kilocycles until it becomes a maximumat the zero voltage point of the oscillator voltage cycle, and thengradually returns to 24 kilocycles.

The modulator output transformer I25 transmits the output of themodulator 20 to the input of the receiver 26.

In the on-target condition, with the output of this modulator a single24-kilocycle frequency, in the receiver this 24 kilocycle wave isamplified by amplifier and changed to a wave of intermediate frequencyof kilocycles by modulator 56 fed from the 1'74-kolocycle oscillator 23,and this 150-kilocycle wave is changed, by modulator 58 fed from the150.8-kilocycle oscillator 60, to an .8-ki1ocycle wave which istransmitted through the'band-pass filter BI and the audio amplifier 62for delivery to the loud-speaker 63 and the audio amplifier 21 inparallel.

When a 24-kilocycle echo signal is being received by R and L with theprojector off-target, the output of the modulator 20 is, as explainedabove, a24-kilocycle voltage with plus and minus deviations from thisfrequency for short periods during the transition times of the voltagecycle of the oscillator 25. Under this condition, but for the effect ofthe inductances and capacities of the receiver 26 the receiver outputwould be similar to the modulator output, i. e., would be an 800-cyclevoltage with plus and minus deviations from the 800-cycle value duringthe transition times of the voltage cycle of the oscillator 25. However,due to the inductances and capacities in the receiver circuit 26, thereceiver circuit characteristics retard changes in frequency, so thereceiver output changes smoothly in frequency, or in other words is afrequencymodulated wave having a modulation rate equal to the frequencyof the 225-cycle oscillator 25, and a frequency deviation from theSOO-cycle means that depends on the amount of frequency shift thatoccurs in the circuit of the modulator 20, which in turn depends on thephase difference between the voltages delivered by R and L. When theprojector is trained on the target, the signal voltages from R and L arein phase, and as indicated above, the output of the modulator 26 is asingle 24-kilocycle frequency. Then, frequency modulation does notappear in the output of the receiver 26, which is a single frequency800-cycle wave under such condition.

A description will now be given, first briefly, then with furtherdetails, of the manner in which the circuit including the frequencydiscriminator 29 and amplifiers 68 and 69, the demodulator 30, theamplifiers 36 and 31, the conjugate input rectifier 40 and the directcurrent amplifier 4|, utilizes the frequency-modulated output of thereceiver 26 to produce horizontal deflections of the cathode-ray beam inthe oscilloscope 42.

The output signal from the receiver 26 is applied to the discriminator29, wherein the phase modulation present in the receiver output causesthe signal to become amplitude-modulated also.

Since the frequency modulation rate is 225 cycles per second theamplitude modulation produced will have a 225-cycle envelope. Thediscriminator output is amplified by the audio amplifier 21 and thenapplied to the full-wave amplitude demodulator or detector 30, whichdetects the 225-cycle amplitude modulation, thereby producing an outputwave component having a frequency of 225 cycles per second. The circuit3| includes a high pass filter and a tuned circuit resonant at 225cycles. This circuit 3! passes only the 225-cycle component of thedemodulator output. After amplification in amplifier 36 this 225-cyclevoltage is applied through conductor 36 to the conjugate input rectifier40. In 40 it is combined with a 225-cycle wave received from oscillator25 through the conductors 38, a phase shifting network I30, theamplifier 31 and the conductors 51. The wave combination produces adirect current voltage which is amplified by the direct currentamplifier 4! to deflect the cathode-ray beam of the oscilloscope 42horizontally.

When the projector is trained from one position to another by passingthrough the bearing of a received echo signal, the sign or direction ofphase shift -between the two projector voltages produced by the signalchanges 180 degrees. That is, the leading voltage becomes the laggingvoltage. Since the amplitude modulation depends on the phase shiftpresent between the voltages from R and L, the amplitude modulation willalso change direction, or in other words, the phase of the 225-cycleoutput of the demodulator will reverse, with respect to the 225-cyclereferi once wave supplied to the conjugate rectifier from the oscillator25 through elements 38, I30, El and 31'.

As pointed out below, there exists a '90-degree phase difference betweenthe 225-cycle voltage of the oscillator 25 and the 225-cycle signaloutput of the demodulator 30. In order that these voltages may becompared in the rectifier 40 to yield the desired results, thesevoltages should be brought into phase. This is accomplished bytransmitting the voltage of the oscillator 25 to the rectifier Mlthrough the phase-shifting network. I36 comprising condenser [31 andresistor E32, and slightly adjusting the frequency of the output circuitof oscillator 25, for example, by its tuning condenser 135, to makecertain tuned circuits. referred to hereinafter work on either thecapacitive or inductive side of resonance.

The 225-cycle signal voltage from conductors S6 and the 225-cycleoscillator voltage from conductors 37 are simultaneously applied to therectifier to. When the projector orientation is in one direction off thetarget bearing the signal input voltage applied to the rectifier 40 willbe in phase with the oscillator voltage applied to the rectifier, andwhen the projector orientation is in the other direction off the targetbearing the signal and oscillator voltages applied to the re. iiier willbe 186 degrees out of The a1 iangement of the rectifier circuits is suchthat the voltages add for one projector position and subtract for theother.

The output of the conjugate-input rectifier it is applied to thepush-pull direct current amplifier ii in such a manner that, when thevoltages add, the plate current in one amplifier tube increases and thatin the other tube decreases, and when the voltages subtract, thedirection of current change in the amplifier tubes is reversed.

The plate current of the direct current amplifier tubes is obtained fromthe 240-volt terminal of source B through the horizontal deflectingcoils t3 and 4 of the oscilloscope G2. When the projector is trained tothe right of its on-target bearing, a received signal causes themagnetic field produced by the change in amplifier plate current throughthe horizontal deflecting coils to be in such direction as to cause thecathode-ray spot to deflect to the left momentarily during its verticaltravel. When the projector is trained to the left of its on-targetbearing the direction of the magnetic field is reversed and the spotwill be deflected to the right. The direction of the defiection of thespot upon reception of a signal is therefore an accurate indication asto the direction the projector must be trained in order to obtainon-target bearing.

Considering the operation of the discriminator 25 and the demodulator 30in more detail, the SOD-cycle frequency-modulated output of the receiver26 is applied to the gain control potentiom eter 28 in the input circuitof audio amplifier 2?, by which the input level can be adjusted to sucha value that deflections on the cathode-ray tube due to noise are lowenough in amplitude to be not objectionable. Signal voltage from thepotentiometer is applied to the tube 63 through the discriminatorconsisting of the series condenser Elli and shunt resistor 56. As the300- cycle frequency-modulated signal impressed across thisdiscriminator varies in frequency, the

1 magnitude of the voltage drop across the conto the ouput of thedemodulator.

denser also varies, because the condenser presents more reactance to lowfrequencies than to high frequencies. This in turn causes the amplitudeof the voltage drop across resistor $5 to vary. Since the frequencymodulation rate is 225 cycles per second, the amplitude of the voltagedrop across the resistor '53 will change at a 225-cycle rate and themagnitude of the amplitude variation will depend on the range offrequency shift present in the SUD-cycle frequency-modulated signal.There is, therefore, applied to the amplifier tube 53 the SEQ-cyclesignal frequency-modulated at 225 cycles per second and amplitudemodulated at 225 cycles per second. This 800- cycle frequency-modulatedand amplitude-modulated signal is amplified in tubes as and t9 and thenapplied by transformer [38 to the full wave demodulator 3G. The cathodesof the demodulator are biased positively with respect to the anodes bythe voltage drop across a resistor I31 which, with a resistor i38, formsa voltage divider connected across the ground terminal and the 22D-voltterminal of the source B. This bias voltage is of such magnitude as toprevent the normal voltages due to noise from passing to the output butpermit any signal voltage capable of producing an indication in theoscilloscope to pass A condenser I39 for by-passing alternating currentis connected across the bias resistor i3l. The demodulator rectifies thesignal and thereby develops a signal output voltage across its cathoderesistor Hill. This voltage is applied through a coupling condenser Mlto a transformer M2 which is resonated at 225 cycles by condensers M3and M6. The condensers MI and I 43 form a low impedance path forfrequencies above 225 cycles per second, While the condenser Hi! and theprimary winding of the transformer I42 form a low impedance path forfrequencies below 225 cycles per second. Therefore the BOO-cyclefrequency modulated output and other unwanted frequencies present in thedemodulator are filtered out and the 225 cycle component (which isdetected amplitude modulation) are transmitted to the amplifier 36 dueto the high impedance of the resonant circuit formed by elements I42,I43 and I44 at this frequency, and so are amplified in 36 and thentransmitted through the conductors 35' to input transformer I50 of theconjugate-input rectifier 413. During an on-target condition thecondenser I4! aids in reducing erratic deflections n the oathode-raytube caused by transients, as it attenuates the signal and blocks thedirect current component from reaching the parallel-resonant circuit oftransformer I42.

Above, it was shown that maximum frequency modulation (1. e., maximumfrequency deviation) occurred at the instant the 225-cycle voltage ofthe oscillator was passing through the zero voltage point of its cycle.The maximum amplitude of the 225-cycle signal output of the demodulator38 occurs at this same instant, since this maximum amplitude occurs atthe instant of maximum frequency modulation. Therefore, there will be adifference in phase between these two 225-cycle voltages of 90 degrees.

As will appear from description, hereinafter, of operation of theconjugate-input rectifier 40, it is desired to have the 225-cyclevoltage that is applied to the conjugate rectifier either in phase or180 degrees out of phase with the voltage from oscillator 25 that isalso applied to this rectifier. This condition can be attained byintroducing appropriate phase shift. For example, this phase shift maybe made to occur principally at the phase shifting network I353comprising the series condenser IN and the shunt grid resistor I32 andat the transformer I42. Due to the small capacitance of the condenserI3I, the voltage applied to the amplifier 31 will be shifted in phasefrom the voltage of the oscillator 25, and, taking into considerationphase shifts ocurring at various points in the signal circuits, thephase shift of the network I30, which may approximate 90 degrees, verynearly brings the signal and 0scillator voltages into phase. The finaladjustment may be obtained in the resonant circuit of the transformerI42 by slightly changing the frequency. of the oscillator 25, forexample by adjustment of its tuning condenser I35. Changing thefrequency of this oscillator likewise changes the frequency modulationrate, and the amplitude modulation derived from the discriminator willlikewise be at the new frequency of the oscillator 25. By shifting thisfrequency in the proper direction from the 225-cycle resonant frequencyof the circuit comprised by the transformer M2 and its associatedelements, the output of this transformer can be made more or less out ofphase with its input. With a slight adjustment of oscillator frequencyit is therefore possible to make the voltage from the oscillator 25 andthe signal voltage either in phase or 180 degrees out of phase at theconjugate-input rectifier, the relationship depending on the directionthe projector is turned from itson-target bearing.

The above detail d operation of the circuit including the discriminator29 and the demodulator 35, is for an off-target condition, i. e., acondition in which the output of receiver 26 supplies an BOO-cyclefrequency-modulated wave to the discriminator. Before detailing theoperation of the rectifier es and direct current amplifier 4| for theoff-target condition, the operation of the discriminator 29 and thedemodulator 3| for the on-target condition will now be detailed. The re.

from 225-cycle modulation. This signal is amplified by the tube 69,rectified by the demodulator 38, and finally filtered out in the outputcircuit of the demodulator and the resonant circuit of the transformer I32. Since there is no 225- cycle modulation on this signal, there willbe no output from the transformer I42. The input to the rectifier G6will be only the voltagefrom the oscillator '25. In other words, theconjugate input rectifier 4B, and so the direct current amplifier 4|, isnot affected by the signal. Consequently, the oscilloscope spot is notdeflected from its vertical travel. That is, when a signal is receivedthe spot continues to travel vertically Without significant deflection,showing only a brightening effect due to the application of some of thesignal voltage as a brightening voltage.

Considering, now, detailed operation of the circuit of the conjugateinput rectifier 4H and the direct current amplifier ll, this circuitcomprises a rectifier tube I5I feeding direct current amplifier tubesI52 and I53 through a network I60 of resistors and condensers includingresistors I BI I52, I63, I54, I65 and IE6 and condensers I61 and I68.The 221-cycle signal from the buffer amplifier 36 is applied to theplates of the rectifier tube I5! through the conductors 3B and the inputtransformer I52. A 225-cycle switching voltage from the oscillator 25 isalso applied to these plates by conductors 31', through the center tapof the secondary winding of the transformer I56 and the junction ofresistors IBI and I 52. The rectified resultant of the combined voltagesis applied through the network ISO to the grids of the tubes 952 andI53. These grids are maintained at a negative bias with respect to thegrounded cathodes of these tubes by a voltage divider comprisingresistors I15 and I15 connected to the volt terminal of source B. Thisbias is sufficient to limit the plate current of these tubes to a lowvalue. When a voltage from the network ISO is applied to these grids thebias increases on one and decreases on the other. The plate currenttherefore increases in one of the deflecting coils 43 and 44 anddecreases in the other, thus causing the oscilloscope spot to bedeflected horizontally due to the resulting change in the magneticfield. The detailed operation of the circuit may be considered underthree operating conditions as follows:

(1) The on-target condition when no 225-cycle signal voltage is producedor applied to the rectifier and only the voltage from the oscillator 25is applied to the rectifier;

(2) The off-target condition when the signal voltage and the oscillatorvoltage are applied to the rectifier in phase; and

(3) The off-target condition when the signal voltage and the oscillatorvoltage applied to the rectifier and degrees out of phase.

In condition (1) a 225-cycle voltage from the conductors 31 is appliedto the plates I11 and I18 of the tube I5I through the center of thesecondary winding of the transformer I50 and the two halves I1! and I12of that winding. The voltages on these plates therefore are in phase andare equal at all times. During one-half of the nat g current cycle,current will flow from :res'istor It3:through coil I.II', plate 111,cathode 118?! ,cand resistor I6I Current willalso flow from :resistorI13 through coil I12, plate. I18, cathode 1 1 88 .aand resistor [.62.These currentsiare equal andzzproducev equal voltages across theresistors il'ETI :an'dnl62. These'voltages acrosszresistors Ifilea-ndltfiz chargecondensers I61 and IE8. These resistors give thecircuita long time constant, 'so these condensers will .only discharge'a small :amount during the succeeding half cycle whencurrentdoesnot'fiow through tube I51. A direct current voltage fis;thusmaintained across each C01 theicondensers 161 :and I 68. Since thecurrents :fflowing through the:res'istors NH and I62 are in:opposite'directions, the voltages developed opposei-eeach'other,..and.rass.they .are equal in magnitude,zerovoltageexistsbetween the cathodes I81 and 4B8. :Thevoltage-dropacross resistors I65 and iiififii:isthereforeczero and the grid-cathodevoltage -of tubes l'52 and I53 will be unaffected and remain atitscr'iginal high-negative grid-bias value.

EGonsidering condition .(2) the 'poling of the .primary windingof thetransformer I50 will be assumed to besnchthatfor'the half-cycle of theivoltagegfrom oscillatorr25 in which .therectifier 1E5 lzconductsthevoltage inducedin-the secondary ewindingywillsbe in a direction to makeits terminal .connec'ted to plate H-I positive withrespect to'Litsi-terminalconnectedtoplate I18. During this RhQlfr-CYOIG'TOfJthCoscillator voltage the oscillator and 'signal voltages are in the samedirection in wcoilfl'H buttaare in opposite .directions in coil I12.Therefore; the-voltage drop across resistor IBI exceeds that/across 152,which is; of opposite sign. lconsequently, .current will flow fromcondenser :IB'I zthrough, resistors I63, I55, I66 ;,and I64 to:condenser 168. Thus,:resistors I 65 and I 66 being ..-,eg:ual,the-potential ofthe grid of tube I52 with :respect --;to itsgrounded :eathode .is driven in *a positive. direction and thepotentialof the grid of -tube I53-withrespect to its grounded-cathode isz'driven anequal amount in the negativedirection. :FIherefore-the platecurrent of tube =I52 increases :and that-:of tube 153 decreases. .Sincethe cur- ;rerrt-s through the like coils 43 -and44 are no filongerequal, their magnetic fields ,no longer cancel, :and: the": spotdeflects horizontally.

-Qperationunder-condition (3) iswthe sameas :undercondition (2) exceptthat, for ithe-ha-lfcycle of the-voltage from oscillator 25 in whichitherectifier-tube :I5I conducts, the oscillator and (signalvoltages areinphase in coil I72 and in -phaseopposition in 0011- HI and:consequently the polarity throughout rectifierand amplifier system istheireverseiof thatfor condition (2). Thus the grid of tube I52 isdriven-in'a negative instead of a positives direction, and the grid oftube I53 is drivenr-in a positive instead of a-- negative .direcztion.-ieonsequently the horizontal deflection of the-oscilloscope spot isoppositeto that .which obtained for condition (2) '.:Thus,:t by:notingthe deflection of-the spot, the

--:fdirection of deviation .of the bearing of the projector from thedirection of the-received sound ,torifrom thei'bearingof :theitarget isapparent. Whiletheabove description has assumed that during the:onatarget condition the spot willhave :nohorizontal'motion, due tocertain transient :conditionsordinarily areceived signal may then causea s'lightzerratic spot deflection-which however is of no :practicalsignificance. A slight "projector bearing deviation fromthe on-targetbeari'ng, as for example a deviation of one degree, will produce anoticeable horizontal-deflection in one direction only.

The distance from the :bottomaof the vertical sweep of theloscilloscopeispotrto the point in :the upward vertical. sweep at which thehorizontal deflection occurs is: proportionalito, or a measure of,thertime that thesoundpulsecausingithe horizontal deflection has .taken'to travel from the projector to the target eand back, or in other wordsis ameasureaof the rangezofzthe target or the distance to theitarget.A:scale '(not shown) maybe provided, along the vertical sweep' path ofthe oscilloscope spot, calibrated in yards, for example, so that theposition :of the horizontal deflection along theverticalzscale'indicates approximately, ;for :anygiven adjustment of.-the range --potentiometer, :the range .of "the-target.

is-indicated above; in :echo ranging the :tele- -:phone receiver orloud-speaker 63 is useful for observing :the strength of :receivedechoes and therefore the .approach'to. or recession from the err-target.conditiomii. e., 1 the projector bearing 'for which theechoisamaximum.The receiver 53 .isuseful ialso forisound listening to 1 determine thebearing zof zany source -of noise such asi-propeller rongmachineryinoisefrom ian enemy ship, torpedonoise, etc, thebearing 1or:direction-ofapproachofsuch noise being -determined-ras-that-projector"bearing inwhich the soundg-received in the device "5:? is loudest. For

this isonnd listening, underwater sounds may-be 'iobserved throughoutthefrequency range l0kil0- cycles". to :30 'kilocycles; for example. Thismay be 1done bychanging, the tuning of:the -,0S.G.i11ator 23 and the,amplifier 55 simultaneously, f or instance, :=by-1the pganged condensersC23 and C55 shown adjacent the devices :-23:and 55, as representing J-telegraphic"communication. This can-be obtain- ,edbetweenships,equippedwith the-bearing deviationindicator, byz-causingthe keying circuit =-32'-tokey the operating circuit of the relay inaccordance with the desired telegraphic code. .The system receivescontinuous wave or modulatedrcontinuous wave telegraph signals.

The-broad frequency band of transmissionof 1 the projector makes:possible a choice of the sound frequency,'in transmission andreception, that is .:not=only,useful inconnection with simultaneousoperation of the .bearing deviation "indication -;equipment;providedon-several ships'in the same ;area, butalso givesa considerable controlover the directivity of the projecton'since the projector iswmoredirective-at the-high frequencies of its transrnissionrrange thanat the .low frequencies. The :widefrequency range is also :of particularvalue ;-in;ilisteningrto soundssuch as propeller-and ma- :chinerysounds. .Moreover, the ability to select the sound frequency to be usedin transmitting {and receiving telegraph signals makes availableadditional telegraph channels.

Fig.4 shows a modification of the bearing deviation indicating system ofFig. l which uses die-frequency modulation and includes no fre-.:quency.:discriminator circuit such as the circuit "29 oflFig. l.Aprojector 3, divided into two parts It and'L serving as thereceiving'pick-up devices .or hy'drophones,-may be, for example, of thecrysitalatype referred to in connection with Fig. 1, the

' direct current milliammeter.

bearing deviation indication being obtained from the phase difference ofthe voltage outputs of R and L, as in the case of the system of Fig. l.A deflection or visual indication having the sign or sense of this phasedifference, and having a magnitude proportional'to this phasediflerence, may be obtained in a zero-center indicating device 242, asfor example, a cathode-ray oscilloscope or a If an oscilloscope is used,it may be, for example, of the type shown in Fig. 1, the horizontaldeflection of the cathoderay spot indicating the projector bearingdeviation as in the case of Fig. 1, and the vertical sweep circuitbeing, for instance, as shown in Fig. 1.

For operating the indicator 242 in response to the signals from R and L,a circuit comprising a system of modulators is used. The circuitincludes a pair'of transformers H and 2H6 fed from R and L and feeding apair of modulators Zill and 202 each of the duplex or balanced type, anamplifier or receiver circuit 226 fed by the modulators 29! and 2&2, ademodulator 239, and a conjugate-input rectifier or phase-sensitive,amplitude-sensitive detector 249. An oscillator or alternating currentsource 225 supplies modulators ZEI and 202 with voltages c3 and -e3, re-

spectively, which may have a frequency of 225 cycles per second forexample. The source 225 also supplies the voltage (23 to the rectifier24B. Thereceiver 226 is fed not only by the modulators 26! and 202, butalso by a phase shifter 295, which is supplied with voltages from R andL through tertiary windings on the transformers 2l5 and 2l6 and whichintroduces a 90-degree phase shift in those voltages in transmittingthem to the receiver 226. If desired, the connections (shown dotted)between projector 3 and transformers 2 l5 and 2| 6 may be the same asthe connections shown in Fig. 1, between the projector 3 and thetransformers I 5 and i5, and the means for transmitting the sound pulsesor signals may be as described in connection with Fig. l.

The signal voltage outputs from R and L are designated ea and 61.,respectively. ,.They need not be restricted in any manner except thatthey must be of the same frequency. However, to simplify themathematical derivation below, it is there assumed that they are equalin magnitude but may differ in phase by an angle 0. The equations forthese output voltages, designating their frequency as 29/21:- and theirmaximum instantaneous magnitudes as E, are:

R=E sin pt I (1) EL=E sin (pH-0) These signals ea and en are introducedinto the balanced modulators 2M and 202, respectively, into which,respectively, are introduced the voltages eg and -e3, of frequencyq/21r, the equation for ex being es=E3 sin qt Assuming ER. and E1. to beequal in magnitude, the outputs from these modulators will be:

These outputs can be combined either additively or subtractively, bytransformers 296 and 291, for example, to give in the input of thereceiver 226:

[(pq) [(p+q) +g+g]] Likewise, the original signals can be combinedeither additively or subtra-ctively, by the tertiary windings oftransformers 215 and 216, for application to the input of the receiver226. If they are not shifted in phase, (i. e., if the phase shifter 295be omitted), the results will be:

0 9 e e =2E Sin 5 sm (pt+ (8) However, with the -degree phase shiftintroduced by the phase shifter 295, the results are:

e' e' =2E sin sin mg) 10 In the input of the receiver the outputs of themodulators are combined with the original signals to give e6. Thisvoltage is amplified and demodulated in the receiver 226 and thedemodulator 230 to give its envelope, which will contain a voltage offrequency that appears as-c'z in the output of the detector 230.

The value of 6s depends upon thte particular manner in which itscomponents are combined. The following tabulation shows the possiblecombinations making up eeand the resulting value of 67.

The most useful combinations for the purposes of bearing deviationindication are given in the expressions (15) and (18). In these twoexpressions the amplitude of the voltage a7 is proportional to the sineof the phase difference between the original signals ea and CL.Therefore, either of the two corresponding values of 66 can be used togive a right-or-left indication in the device 242, by introducing thecorresponding voltage e7 into a conjugate-input rectifier orphase-sensitive detector 240 to which the voltage ea is also supplied asindicated above.

Fig. 5 shows a circuitsimilar to that of Fig. 4 but having modulators30! and 382 with phaseshifting resistors R1, R2, R'1 and Rz-andcondensers C1, C2, U1, and C'z insteadof the modulators 20I and 262 andthe phase shifter "295. Without these elements each of the...moclu1ators3 I and 36-2 :isamodulator ofv :usual ring. or double-balanced type.The'modulator 236 has input transformers 3I5 and T and outputtransformer T1. The modulator 392,-haszinput transformers 3I6 and T andoutput transformer Ti. Z'Ihe voltage eapobtaine'd as inthecaseof thesystems ofFigsml and 4,15 applied to'the primary .mwinding of the inputtransformer 3E5 for the .modulator 3M, and transmitted, through coils..systems Qf FigSfil and-4, is applied to the primary winding of thefinput transformer 3&6 for the modulator 3532, and transmitted, throughcoils 515A and-16B forming the xtwohalvesof the secondar Winding, to thebridge-network of copperoxide varistors or-rectifiersZA, 2B,2C'and 2Dshunted' by the elements C 1,R1, C'z, R'-'2, respectively.

The. oscillator orssource- 225::feedstt'o the primar windings of thetransformers T and T .waves whichinduce'in their. secondary windings"the voltages es and ='.e3, respectively. The source 225 also suppliesthe voltage e; to therectifier 25.0.

The output voltages'e4 and 6'5 of the modulators 39I and 302 combine toproduce incthe input ;;of the receiver 226'the voltage wee having eitherof the values indicated in the expressions (15) and (18); and the systemofFigJB operates in the same manner as the system of Fig. 4 to producefrom this voltage 66 applied to the receiver 226 and the voltage 63applied to the conjugate-input rectifier, the desiredindication in theindicating device 242.

The modulators3fll and 392, with'tneir associated phase shiftingelements R1, C1, R2,Cz, R'i, Ci, R'aand '2, operate'to transmit theoriginal signals enand 61. with a 90-degree phase shift and combine themwith the modulation products that would appear in the output circuits ofthe modulators in the absence of the phase-shifting elements.

The-modulators30 I-and-3fi2in-theabsence of the; phase shifting elementsB C1, R2, C2, Ri, C'1, R'z, and C52 vwill :not transmit the originalsignals ea and er. to the amplifier 226. These phase "shifting elementsoperate "to unbalance this bridge action ..and transmit It/he gsignalsea and 31.170 amplifier "226 in propor.tion to the degree of unbalance.If the'phase "shifting elements are chosen so that the in-phasecompon'rits'of the" transmitted waves 6'4 and 6'5 are equal in magnitude'and'opposite in sign, which can be done by methodswellknown in the art,the rresult will be to ,transmita wave which;is :effectively shifted, 90degrees in -phase' relative to the sum of the two voltages errand en.

The modulator 20 ofiFig. l'may be viewed as formed of .two: zmodulators,one comprising 'varistors I2I and I22 excited in parallel from thetransformer I5 and inseries. from the winding I21, and theother-comprising ,varistors I235 and I24 excited ,in-parallel from thetransformer I6 and in series from "the coil I21. ,As shown, the primarywinding of the output transformer I25 is commontto these two modulators.However,

..ifrdesired,ithe;,mid point ofrthis windingmay be "conductor (notshown) without 'materially: affecting the operation of .-the modulatorcircuit since these two points/are equipotential points. The outputo-fthe one modulator-may'belviewed -.asthe-voltagelbetween the junction of-varistors I2I and I22 and the junction-of thelsecondary wi-ndings oftransformerslfi and I6, and maybe designated e"4; andthe output-oftheothenmodulato-r may be viewed as thevoltagelbetween-the junction ofvaristors I23 and IZkand the :juncvtion of the secondary windings oftransformers IE-and-IB, and-maybe designatede"s. v The voltage'acrossthesecondarywinding of transformer :I25 -may be their sum, e 4+efe, andmay be designated e"s. :For simplicity,thejreceiver.26..andpotentiometer 28 may be omitted, the ampli- .fier 2'I (andfrequency discriminator 29) then hbeingresigned tooperate atthe24ekilocycle .fre-

.quency level instead of, at theBOO-cycle frequency level. Then "4 1 zi+k2612 a CH5=IC1GL 'k e;,e

" This value of 1 e"6 is the same as the value-of res "giveninexpression (11)..

' Thus,

-'I-his' voltage efe -is fdifferentiated :by the frequency discriminator:29. Designating :-,the acapacity'ofthe condenserr asC, its 'reactance'as .Xc;.the resistance of the-resistorJEB as -R, .-the current flowingthrough-the .condenser-z and the resistance (due to 6 673.5 ietheresulting voltage acrossthe resistance ase srand the conse- Mquent..225-cyc1e output voltage .of the. detector .30 (that is, the-envelopeof :e"..s) as-e.-1,.then'if Xc R,c it follows that:

6 z a tP+q)- [(P'I'QM'I] and the voltage e'vof frequency 7 i 2w ..is

;e =KE E -sin dpq cos qt =K sin 0 cos qt 24) which is of the correctform to introduce in the rectifier 40, together with the conjugatelyintroduced input voltage e3 L,'to obtain a direct current output whichwill vary with a 0.

What is claimed is:

1. A system for'indicating the sign'ofthe phase angle between a firstvoltage 'andasecond'voltage comprising four two-terminal rectifyingdevices connected in series, forming a closed circuit and being poledin'the same direction in the closed circuit, a coil for-applying a thirdvoltage of lower frequency between the "junction point of one pair ofsaid rectifying devioesa'and the junction point of the other pair ofsaid rectifying devices, means for applying said first voltage betweenthe mid-point of said coil and a junction between said pairs, means forapplying said second voltage between said mid-point and the otherjunction between said pairs, a circuit comprising frequency demodulatingmeans connected across said two latter junctions to produce ademodulator output voltage having said lower frequency, aphase-sensitive detector network having two input branches, and meansfor applying to one of said branches said demodulator output voltage andto said other branch a voltage which is approximately in quadrature withsaid third voltage and which'is in phase with said voltage applied tosaid one branch when said phase angle between said first and secondvoltages has one sign and in phase opposition to said voltage applied tosaid one branch when said phase angle between said first and secondvoltages has the opposite sign.

2. A wave receiving system comprising a pair of like adjacent hydrophonereceivers for receiving an underwater sound wave of given frequency,having substantially the same amplitude but a different phase at the tworeceivers, means connected to said receivers comprising four rectifiersconnected in series, forming a closed ring modulator and being poled inthe sam direction in the ring circuit, a coil for applying a thirdvoltage of lower frequency between the junction point of one pair ofsaid rectifiers and the junction point of the other pair of rectifiers,means for applying said first voltage between the midpoint of said coiland a junction between said pairs, means for applying said secondvoltage between said mid-point and the other junction between saidpairs, an amplifier and receiver connected in the output of saidmodulator, an amplitude indicator and frequency modulation discriminatorrespectively connected across said receiver, said discriminatorproducing an amplitude modulated output voltage having said lowerfrequency, an amplitude demodulator, a phase- 'sensitive detectornetwork having two input REFERENCES CITED The following references areof record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,564,303 Wold Dec. 8, 19252,144,655 Hahnle Jan. 24, 1939 2,166,991 Guanella July 25, 19392,205,843 Caruthers June 25, 1940 2,305,614 Goldstein Dec. 22, 19422,333,322 Levy Nov. 2, 1943 2,403,727 Loughren July 9, 1946 2,410,386

Miller Oct. 29, 1946

